1. Field of the Invention
This invention relates to a visual communication terminal (namely, an image terminal or a video terminal) having a function of performing a multiplex transmission of images (namely, still and moving images), sound, audio, text or the like by using communication circuits.
2. Description of the Related Art
When conventional visual communication terminals communicate information generated by using multimedia including images, sound, audio, text or the like, a user of one of the terminals (hereunder sometimes referred to as a calling terminal) first sets a telephone number of the other terminal (hereunder sometimes referred to as a called terminal) in a keying portion of the calling terminal by keying the number. Thereafter, when a telephone-number transmission key is pushed, a call control processing portion of the calling terminal performs an operation of connecting the calling and called terminal with a communication circuit through a network interface portion. Then, what is called a communication rate (namely, a communication speed or transmission speed) of sound information is inputted from the keying portion according to the CCITT (Consultative Committee for International Telephone and Telegraph) Recommendation H. 221. Further, the allocation of communication circuits to channels, as well as the frame structure of each of information signals representing sound information, image information and character information, is determined according to the inputted communication rate. Next, according to the BAS (Bit-rate Allocation Signals) code of the CCITT Recommendation H. 241, the frame structure used in and the capability of each terminal are interchanged between the calling and called terminals and moreover, the communication mode of communication therebetween is indicated.
In case where the conventional visual communication terminals communicate with each other by using a plurality of communication circuits, the aforesaid process is repeatedly performed plural times, the number of which is equal to that of the communication circuits. Thus, the conventional visual communication terminals are connected with the communication circuits and communicate information generated by using multimedia which includes images, sound, audio, text or the like (namely, perform what is called multimedia communications).
Further, for example, in the Japanese Unexamined Patent Publication (Kokai Tokkyo Koho) Official Gazette No. H4-96562, there has been proposed a conventional method. Namely, in case of this conventional method, when a call originated from a calling terminal is established on a first circuit connected between the calling terminal and a called terminal, the called terminal transmits a telephone number thereof corresponding to another available circuit (namely, a second circuit) connected thereto, on which no call is established, to the calling terminal by using the first circuit. Then, when the calling terminal receives the telephone number corresponding to the second circuit, the calling terminal automatically dials the received telephone number to thereby establish a call on the second circuit between the calling and called terminals (namely, between calling and called parties).